The present invention relates to a self-bonding magnet wire having good self-lubricating properties.
Manufacturers of electric apparatuses have conventionally omitted or simplified the varnish impregnating step by using a "self-bonding magnet wire" which comprises an enameled conductor having an outer coating that can be fused to an adjacent wire with heat or a solvent. Recently, these manufacturers have come to use high-speed automatic winding machines to increase the speed of the production line. The increased line speed at first seemed to cut the production cost by a substantial degree. However, as it turned out, the gains in production were more than offset by costs incurred as a result of damage caused to the wire and coating by friction and other mechanical stress during the high-speed winding. The damaged coating can effect bonding of adjacent wires such that wires wound tightly into a coil easily come loose and the intended performance of the self-bonding magnet wires is impaired significantly. As another problem, if such damaged wire is assembled in an electric machine, layer shorting (short-circuiting between wires) occurs and the loss factor is increased to an undesirably high level. To minimize the mechanical damage to the self-bonding magnet wire, wires having good self-lubricating properties have been demanded. This demand should be met not only by the automatic winder but also when self-bonding magnet wires are inserted manually into a small slot in a motor.
Since self-bonding magnet wires themselves do not have good self-lubricating properties, the low slip properties between individual wires, between wires and the winder and between wires and the electric machine into which they are assembled cause mechanical damage to the self-bonding layer. Furthermore, the friction may damage the wire enamel or decrease the efficiency of the winding and assembling operations. This problem has partly been solved by coating the self-bonding magnet wire with a layer of various liquid lubricants such as liquid paraffin and refrigerator oil. But the resulting wires still do not have satisfactory lubricating and slip properties and cannot be handled efficiently in manual operation, and what is more, they cannot be wound into a neat coil for making, e.g., a transformer. As the speed of the automatic winder has been increased further and the use of an inserter to achieve a higher space factor is more common these days, insufficient bonding of the magnet wires has become another factor which increases the chance of layer shorting. Improving the self-lubricating properties of wires by applying a large quantity of liquid lubricants is not very effective. In addition, the use of such lubricants causes more dirt to collect on the wires and the bonding strength of adhesive tape used to fix the end of the coil is adversely affected.
Attempts have been made to eliminate these defects by coating the enameled wires with solid lubricants such as solid paraffin and carnauba wax having better lubricating properties than liquid lubricants. To form a uniform coating, the solid lubricants are usually applied to the wires from a solution having a few percent of the lubricant dissolved in solvents such as petroleum benzine, toluene and xylene. However, the use of a large quantity of low-boiling solvents is not only hazardous to human health but with some types of wire, the self-bonding layer dissolves or swells in the solvent. This causes total or partial loss of bonding ability or may cause creases to develop in the enamel layer. Therefore, the coating of solid lubricants can only be applied to limited types of electric wires.
Another method that has been proposed for providing self-bonding magnet wires with high lubricating properties is to use enamel compositions containing synthetic resins having good lubricating properties such as polyethylene, polypropylene and polytetrafluoroethylene, as well as silicone oil, fluorine containing surfactants, and liquid and solid lubricants such as paraffin wax, carnauba wax and montan wax. However, solid lubricants and synthetic resins such as polyethylene, polypropylene and polytetrafluoroethylene are insoluble or sparingly soluble in solvents for the enamel and are difficult to disperse in the enamel uniformly, and the resulting enamel is not highly soluble. What is more, these solid lubricants and synthetic resins are not highly miscible with the self-bonding materials in the enamel. Therefore, it is difficult to disperse them in the self-bonding layer uniformly. Accordingly, the resulting coating does not have a good appearance. Liquid lubricants in the enamel provide a coating whose slip and self-lubricating properties are as low as those of the coating formed by applying them onto the wire.